A direct injection fuel injector has a nozzle end that typically is disposed in and sealed to a through-hole in an engine cylinder head leading to an engine combustion chamber. Fuel is injected into the space of the combustion chamber where it mixes with air to form a mixture that is combusted to power the engine. The severe nature of this environment imposes demanding requirements on the sealing of the injector nozzle end to the through-hole. A commercially acceptable seal must have a useful life at least equal to that of the engine, while tolerating direct exposure to the pressure, temperature, and chemistry of the combustion process. Moreover, in the vicinity of the fuel injector's nozzle end, the seal may be the sole contact between the large thermal mass of the engine and the body of the fuel injector, and hence the sole path for conductive heat transfer from the nozzle end of the fuel injector body.
A known seal that has been used for such application is a flat metal crush washer, typically aluminum or copper. While such a seal is relatively inexpensive and possesses good thermal conductivity and sufficient softness to be crushed into an effective thermally conductive sealing device for this application, its crush characteristic can at times work a disadvantage. Why this is so will now be explained.
The seal may be considered like a spring element that, upon being compressed axially urges itself against respective shoulders on the fuel injector and the cylinder head as it is being crushed to sealing contact with the two. This crushing occurs in response to the application of what typically must be a relatively large installation force for retaining the fuel injector body on the cylinder head.
Because of space constraints proximate the cylinder head, the force may have to be delivered to an end of the fuel injector body that is opposite its nozzle end, and consequently the fuel injector body may be stressed in unpredictable ways that affect its internal parts. For example, precision alignments and clearances may change in unpredictable ways leading to potentially adverse effects on performance, especially if the magnitude of the stress-induced force approximates that of the assembly force which holds the various parts of the fuel injector together. In an engine that has multiple combustion chambers and fuel injectors, the development of random retention forces may also create unacceptable injector-to-injector variations. The problem is compounded when the materials of the fuel injector body and the cylinder head have different coefficients of thermal expansion, such as in the case of an aluminum cylinder head and an injector body of ferrous material.
Alternative forms of seals that do not rely on the development of large axial forces to effectuate the sealing action, i.e. radial seals such as o-rings, V-seals, lip seals, etc., are beset by certain disadvantages that may involve one or more of the following: higher cost, poorer thermal conductivity, poorer tolerances, and more difficult installation.
The present invention retains the use of axial force to develop the required sealing action, but does so without accompanying disadvantages such as those mentioned above. Briefly, the seal that is employed in accordance with the principles of the invention may be considered an eyelet-shaped part that can be squeezed axially to fit into the same annular space, or cavity, as a radial seal. The axial tolerance of the cavity and the characteristics of the eyelet-shaped part can be controlled so that over the expected tolerance range and the expected thermal expansion, proper sealing will be obtained. The eyelet-shaped part has a relatively low spring rate in comparison to a crush washer so that acceptable sealing is attained with the application of relatively low axial retention force on the injector. This avoids unduly stressing the fuel injector body and disrupting the precision relationships that are internal to it. The eyelet-shaped part is a resilient metal ring that is preferably plated with a thin coating of a relatively softer metal, such as zinc, tin, or cadmium, so that abutting part surfaces do not have to have perfect surface finish. The cost of making the eyelet-shaped part is economical because it can be fabricated from a metal like steel by metal forming techniques such as stamping. Because the eyelet-shaped part is thermally conductive metal, it provides a heat conduction path from the nozzle end of the fuel injector body to the engine cylinder head.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings illustrate a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.